Method of controlling the pick-up and drop-away values of mercury switch relays



Oct. 12, 1937. c. H. LARsoN 2,095,604

METHOD OF CONTROLLING THE PICK-UP AND DROP-AWAY A CH RELAYS VALUES OF MERCURY SWIT Filed Aug. 24, 1935 Patented oet. 12, 1937l 2,095,604

UNITED sTATEs PATENT OFFICE METHOD F CONTBOLLING THE PICK-"Ul" AND DROP-AWAY VALUES 0F MERCURY SWITCH BELAYS cari n. umn, Elkhart, nld., miglior' to The Adlake Company, a corporation oi.' Illinois Application samt 24, 193s, serial No. .37,123 achim. (ci. zoe-nz) Electromagnetic relays have a great variety of of Figs. 3 to 13 inclusive affect the pick up and uses. Ihe operating characteristics of any pardrop away values of the relay.

ticular relay are determined by the power avail- At the outset it should be specifically underable and the function that the relay is to perform. stood that the illustrations and descriptions of In some cases, the relay is required to operate specific forms of electrodes are for the purpose 5 within relatively narrow ranges of voltage of complying with Section 4888 of the Revised changes; in other cases, a relatively large diii'er- Statutes and that the invention is not limited to ence between pickup and drop away values is de-v these forms or any of them unless required by" sirable. the prior art.

To a limited extent, the desired operating char- The utility of this invention is illustrated by its 10 acteristics may be obtained by adjusting the air application to a relay of the mercury displacegaps in the iron circuit, by increasing or dement type which comprises a relay coil 20, an creasing the power consumption of the relay, iron circuit 2l and a mercury switch 22. The 'and by controlling the conditions under which switch 22 comprises a glass envelope 23 containl5. the relay is made to operate; but there are limiting a quantity of mercury 24 and through the 15 ing factors which sometimes make it very diflicult base of the envelope electrodes` 25 and 26 are to obtain specified operating characteristics. sealed. Electrode 25 is covered for a portion Ih electro-mechanical relays it is necessary to of its length by an insulating sleeve 21 that is establish a minimum air gap in order to guard fused to both the electrode 25 and the switch zov against relay failure due to remanence in the iron envelope. Preferably the switch envelope 23 and 20 circuit. The air gap, as thus determined, necesthe insulating sleeve 21 are made of high grade sarily limits the sensitivity of the relay. Furtherborosilicate glass, as for example, that disclosed more, it is necessary to employ sumcient power in Weintraub, Patent No. 1,154,081, issued Sept. in electro-mechanical relays to overcome the ef- 2l, 1915. y

z5 fect of contact resistance. A displacer v28 of iron or 'other suitable mag- 25 In mercury switch relays, however, of the type netic material responds to the iiux set up by the disclosed in Larson, Patent No. 1,967,247, issued coil 2li and displaces more or less mercury, de- Jiily 24, 1934, thereis no contact resistance (at pending upon the state of energization of the least the contact resistance is infinitesimal), and coil 2B. As shown in Fig. l, the coil 20 is dethe minimum air gap is furnished by the glass energized and the mercury level is such that the 30 envelopewhich contains the armature. Hence, bared end 28 of the central electrode 25 is out of it adapts itself more redily i0 unusual design contact with the mercury and hence the circuit requirements. through the electrodes 25 and 26 is open. When I have discovered that the pickup and drop the coil is energized, the displacer is drawn i5 away characteristics of mercury displacement downwardly within the switch envelope as shown 35 relays may be COlltI'Olled Within Wide limits by in Fig. 2, and a suiiicient quantity of mercury is giving due consideration to the shape of the inter- Vdisplaced to bridge the electrodes 25 and ze. mittently immersed electrode and/or the shape For dependable operation the mercury is puriald mteriai f the insulating Sleeve which Sul'- fied prior to its insertion in the switch envelope,

l0'- rounds that electrode for a. portion of its height. .and before the envelope is Sealed off ai; n, the 40 The primary object of this invention,'theref01`e. entire envelope is evacuated of air (the mercury is to determine how the shape of the intermitbeing heated during the process to drive out intently immersed electrode and the material of eluded and occluded gases) and then ued with which it is composed affect the pickup and drop an inert gas such as helium, hydrogen, or the la away values of the relay. mm berlgg 1125022? ggstraengrgcdgstffne vthl Preferably the displacer 2l is restrained by a `spring 3l (when the coil 20 is de-energized) to a gsfvllliitliioniis read of *me accompanying drawmg position within the switch envelope that is some- 0 Figs 1 and 2 are views which wm be used to what below its position of floating equilibrium. 5@ explain thetype of relay to which the invention The me 0f this is t0 make the Tela-i 'imm is particularly applicable; sensitive and to hold to a minimum the power i Figs. 3 to 13 inclusive are fragmentary views of that is required to operate the relay. various forms of central electrodes.' and The iron circuit 2i is of no particular impori5 Iig. 14 is a chart showing how the electrodes tance to this disclosure and sufiice to say that it 56 may be of the type disclosed in Larson, Patent No. 1,967,951, issued July 24, 1934.

Before describing in detail the illustrative embodiments of the invention, it may be helpful to analyze briefly the theory which is believed to underlie the present invention, although all theoretical discussions in this specification are to be construed not as dening a mode of operation, but merely as a possible explanation of-certain physical or electrical phenomena known to exist.

Let us assume that the plunger 28 is in the position shown in Fig. 1 and that suiicient voltage is applied to the coil 20 to bring the mercury level approximately to the top of the insulating sleeve 21. Since mercury has a relatively high surface tension (of the order of 500 dynes per square centimeter) it is actually possible to have th'e mercury level in the switch above the top of the insulating sleeve 21 without establishing contact between the bared end 29 of the electrode 25 and the mercury fill. The force that holds the mercury away from the bared end 29 is a function of the surface tension of the mercury, the area of contact between the sleeve 21 and the mercury, and the coeicient of friction of the material constituting the sleeve 21. Since it is not practical to change the surface tension of Imercury by the addition of chemicals, I control the pickup and drop away values of the relay by varying the area of contact between the mercury and the sleeve, and/or the bared end 29 ofthe electrode, or by varying the material of which the sleeve 21 is composed. The variations in shape and/or material may have the eifect of r shown in Figs. 3 to 13 inclusive, illustrative forms of electrodes which are capable of effecting differences in pickup and drop away values ranging from substantially equal pickup and drop away values to a spread of approximately 25 percent of the normal operating voltage (the electrode of Fig. 3 having substantially equal pickup and drop away values and those in the subsequent gures having progressively increasing diierences in pickup and drop away values, as shown in the chart of Fig. 14).

In Fig. 3 the bared end o-f the electrode 25 is bent over to one side of the sleeve 21 and the tip of the bared end is pointed as indicated at 32.

VThe pickup and drop away values of a switch using this type of electrode are substantially equal'because the ,area of contact between the electrode 25 and the mercury at the moment when the circuit is broken is held to a minimum and the effect of surface tension is correspondingly small.

The electrode of Fig. 4 diiers from that shown in Fig. 3 in that the tip of the electrode is rounded Aas indicated at 33, thereby slightly increasing the effective .area of contact correspondingly increasing the difference between the pickup and dropaway values of the relay.

The electrode of Fig. 5 differs from that in Fig. 4 by having the bared end of the electrode squared off as at Fig. 4 and by referring to Fig. 14,'it will be seen that this electrode raises the pickup and drop away spread to approximately 5 percent.

It will be noticed that when the bared end of the electrode is bent over to one side, the insulated portion of the electrode is set to one side so that the downwardly projecting bared end of the electrode may lie on the longitudinal axis of the switch. The purpose of this is to have the making and breaking of the electrical circuit take place at the exact center of the switch so as to maintain the desired operating characteristics even thoughthe switch envelope may be slightly tilted with respect to the vertical axis.

The electrode of Fig. 6 is the same as that shown in the assembled relay of Fig. 1. Here the bared end of the electrode projects upwardly from the sleeve 21 and the mercury in making contact with the bared end of the electrode must ride over the shoulder 35 of the insulating sleeve 21.

In Fig. 7 a small bead 36 is4 formed on the end of the sleeve 21 and this impedes the flow of mercury to the electrode when the circuit is being closed.

In the electrode shown in Fig. 8, a sleeve 31 of ceramic material such as Alundum, a product of the Norton Company, Worcester, Massachusetts, is fused to the end of the sleeve 21. It has been found that Alundum and similar materials, when used in this manner, increase the spread in pickup and drop away values, presumably because the material is highly refractory and any arcing that occurs when the circuit through the switch is opened has little or no effect in disintegrating the por-tion of the refractory sleeve over which the arc forms. When the electrode is formed so that the arcing takes place over the shoulder 35 of the glass sleeve 21 (as shown in Fig. 6), the shoulder is quickly rounded to the form shown in Fig. 6, with the result that less mercury need be displaced in order to complete the electrical circuit through the electrodes.

In Figs. 9 to 11 inclusive, a glass or ceramic cup 38 is fused to the end of the insulating sleeve 21 so that the end of the electrode 25 is exposed within the cup. 'I'he cup is normally filled with mercury as shown at 39 so that when the switch displacer is lowered, the circuit through the switch is completed over the edge 90 of the cup, this edge preferably being on the longitudinal axis of the switch. I have found that I can control the spread in pickup and drop away values when using a cup of this type by varying the angle at which the cup is cut, for when the cup is cut oii at a. steep angle, the diierence in pickup and drop away values is less than when the cupis cut 01T at a smaller angle.

In Fig. l2` the cup on the end of the electrode 25 is cut away on two sides which obviously in- I creases the spread between the pickup and drop away values.

In Fig. 13 the cup electrode is squared oi so that when the circuit is broken, there is a relatively large area of contact between the two bodies of mercury.

'I'he illustrative embodiments of the invention described above and the explanations that have been made with reference to their effect on the pickup and drop away values in the relay make it clear that greater diierences in pickup and drop away values may be obtained by corresponding changes in the shape of the protective sleeve around the intermittently immersed electrode and similar changes in the material; for example, the thickness of the ceramic cup in the cup electrode shown in Fig. 13 may be increased to Obviously the impedance to the mercury now...

may be accomplished vby means other than the sleeve surrounding the central electrode. All

that is necessary is that the effect of the surface tension of the mercury in the vicinity of the intermittently immersed electrode be made to correspond with the span of pickup and drop away values desired.

'I'hroughout the speciiication and claims, the expressions pickup value" and drop away value have been frequently used, and the following explanation will serve to indicate what is meant by these expressions.

The pickup value of a relay is the minimum voltage which must be applied to a relay coil in order to operate the relay (i. e. open the contacts in a back contact relay, or close the contacts in a front contact relay). If. a lesser voltage is applied to the coil, the relay will not' operate.

The drop away value of a relay is the minimum voltage which will sustain the relay inv its energized position (i. e. keep the contacts open in a back contact relay or keep them closed in a front contact relay). If the voltage falls below the drop away value, the condition of the electrical circuit through the contacts will change.

Both pickup and drop away values are critical, particularly in a mercury switchrelay of the type herein disclosed.

To illustrate the use of the terms, let it be supposed that the coil 2i) in Fig. 1 is connected to a suitable source 'of electromotive force, and that a rheostat and voltmeter have been placed in the circuit in order that the voltage across the coil may be varied at will, and indicated.

Starting with a zero voltage across the coil and gradually increasing the voltage, it will be obv served that when the yvoltage has reached some predetermined value, for example, two volts, the spring 3| will have been relievedof its compression and subsequent increases of voltage will produce a proportional downward movement of the displacer.r As the voltage across the coil is increased, the' mercury level within the switch gradually rises due to the displacement action of the armature 28, and at some critical voltage (pickup value of the relay), say 5 volts, the mercury level will finally reach the bared end 2! of the electrode 25 and close the electrical circuit between the electrodes 25 and 26. Obviously after the contacts have been closed, further increases in the voltage across the coil will not change the closed condition of the electrical circuit through the contacts, although the'armature may be drawn farther down into the mercury.

Now let it be supposed that in the case above, after the voltage across the coil had been increased up to 7 or 8 volts the rheostat isoperated yto progressively decrease the `voltage across the coil. For each successive decrease in voltage, the armature 28 movesupwardly pro portionately, and the mercury level falls a corresponding amount. When the voltage' is reduced to 5 volts the armature 28 occupies exactly the same position that it occupied at that voltage when the voltage was being increased, but due to the surface tension of the mercury, the mercury column will not break away from the exposed end 29 of the electrode 25 until there has. been a further reduction in voltage. For the type of electrode shown in Fig. 1, the break in the electrical circuit will come when the voltage is reduced to approximately 4.6 volts. Inthe illustration given above, the spread between the pickup and drop away valuesis the difference between 5 and 4.6, or ths of a volt.

If an electrode, such as shown in Fig. 13 had been used in place oi' the one shown in Fig. 1, the voltage across the coil, under the same circumstances, would have had to be reduced to approximately 3.8 volts before the circuit through the electrodes 25 and 26 would open.

I claim as my inventioni l. A method of controlling the span between the pickup and drop away values of a mercury displacement relay of the type in which a quantity of mercury is adapted to be manipulated in and out of contact with an electrode, said method consisting in forming' the electrode of such shape that the desired span will be obtained through the eifect of the surface tension of the mercury when contacting the electrode.

2. A method of controlling the span between the pickup and drop away values of a mercury displacement relay of the type in which a quan.

tity of mercury is adapted to be manipulated in and out of contact with a conducting surface of an electrode member having an insulating sleeve, said method consisting in forming said sleeve in such a manner that the desired span will be obtained through the effect of the surface tension of the mercury in contact therewith.

3. A method of controlling the span between the pickup anddrop away values of a mercury displacement relay of the type in which a quantity of mercury is adapted to be manipulated in and out of contact with a conductingsurface of an electrode member having an insulating sleeve, said method consisting in so forming said sleeve as to shape and material that the desired span will be obtained through the effect of the surface tension of the mercury in contact with said sleeve.

4. A method of controlling the span between the pickup and drop away values of a mercury displacement relay of the type in which a quantity of mercury is adapted to be manipulated in and out of contact with a conducting surface of an electrode member having an insulating sleeve, said method consisting in so forming said sleeve a's to its shape that the desired span will be obtained through the eifect lof the surface tension of the mercury in contact with said sleeve.

5. A method of controlling thevspan between the pickup and drop awayvalues of a mercury displacement relay of the type in which a quantity of mercury is adapted to be manipulated in and out of contact with a conducting surface of an electrode member having an insulating sleeve, said method consisting in so forming said sleeve as to its' material that the desired span will be obtained through `the eil'ect of the surface 'tension of the mercury in contact with said sleeve.

6. A method of controlling the span between the pickup and drop away values of a mercury displacement relay of the type in which a quantity of mercury is adapted to be manipulated in `the' pickup and drop away values of a mercury displacement relay of the type in which a quantity of mercury is adapted to be manipulated in and out of contact with a conducting surface of an electrode member, said method consisting in selecting means to produce a surface tension effect of mercury in contact with said member capable of producing the desired span.

8. A method of controlling the span between the pickup and drop away values of a mercury displacement relay of the type in which a quantity of mercury is adapted vto be manipulated in and out of Contact with a conducting surface of an electrode-member, said method consisting in selecting means to produce a surface tension effect of producing the desired span.

9. A method of controlling the span between the pickup and drop away values of a mercury displacement relay of the type in which a quantity of mercury is adapted to be manipulated in and out of contact with a conducting surface of an electrode member, said method consisting in selecting means to produce a surface tension eiect of mercurysurrounding -said member capable of producing the desired span.

CARL H. LARSON. 

